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mikeandbecky · 08-17-2007, 07:53 AM

Im tackling a new project that I know almost nothing about: the Suburban NT 30 MA furnace. The PO apparently had it working ( 11/99 ) however I received the trailer and I found that it is not working. Nothing. The Suburban thermostat on the bedroom wall is in place, but, there are three wires coming from the wall through a hole, right next to the Suburban Thermostat( I am assuming that was another thermostat(?) for (?) maybe the old original Armstrong air conditioner? I now have a Dometic AC with no thermostat.
So, I have tried starting the heater according to the manual, via thermostat. Doesnt work. The gas valve outside the trailer is open( inline with the pipe ). Any suggestions where I should start now?

Thanks. I cant wait for this one.

nickcrowhurst · 08-17-2007, 10:11 AM

As you say you know nothing about the furnace operation, and as the device deals with potentially explosive gas, I would suggest you get a professional to overhaul and clean the furnace, preferably while you watch. This is what I did when I first owned my trailer. Subsequently, I have carried out my own overhauls and repair.
If you are determined to try yourself, I would recommend obtaining the circuit diagram, and then read this thread:

http://www.airforums.com/forums/f427...g-up-3122.html

Before touching the furnace, I would short out the thermostat to eliminate it as the source of the problem. Take care.
Nick.

mikeandbecky · 08-17-2007, 11:41 AM

So Nick,
How would I " short out " the thermostat?

nickcrowhurst · 08-17-2007, 11:58 AM

If the furnace was still installed I would remove the thermostat from the wall, dissconnect the two wires leading to it, and then join them together with a wire nut. This would simulate the stat "calling for heat". You sent me a PM stating that the furnace was now on the bench, so the simplest method is to apply 12v to the time-delay relay coil, and find a ground for the coil ground wire. Further to your PM query about the fan not running:

No, the fan will not run until after about a 20 second delay, as the circuit is controlled by a time-delay relay. This must be checked with a voltmeter. The thermostat switches power to the relay coil. When this coil is energized, current flows across the relay from the "always live" wire to the "switched power" wire, which goes off to the sail switch. The fourth lead is the ground wire for the coil. The relay is usually at the bottom left of the furnace, near the gas control solenoid.
The relay has 4 wires:
1. Thick, always live 12 volts from the main trailer battery.
2. Opposite 1, thick, switched power to sail switch.
3. Thin wire carrying 12v to relay coil when thermostat calls for heat.
4. Thin wire opposite 3, ground from coil.

The relay incorporates a 20 (approx) second delay. They are cheap and easy to replace. The relay is just a switch.
I am assuming that your furnace is similar to mine, of course.
Nick.

mikeandbecky · 08-17-2007, 03:09 PM

I think my fan motor is burned up. It wont respond when using a jumper wire.

nickcrowhurst · 08-17-2007, 03:13 PM

Did you definitely bypass the sail switch and limit switch and get direct on to the motor?
Nick.

nickcrowhurst · 08-17-2007, 03:30 PM

You may find this thread informative:

http://www.airforums.com/forums/173469-post5.html

Nick.

mikeandbecky · 08-17-2007, 04:29 PM

Heres what I did: I located the two wires from the fan motor ( pos and neg/ red and black ) . Using a 12 VDC car battery, charged to about 12.9 volts, I connected jumper wires -- Pos. batt. to red motor wire, neg batt. to black motor wire, and....nothing. Is this right? Or do suggest another route? Thanks for the help, Nick.

nickcrowhurst · 08-18-2007, 12:56 AM

Mike, we're 7 or 8 hours ahead of you in the time zones here in the UK, so I've been in the land of nod. Provided the fan spins freely by hand (no mud daubers etc), and you were applying the 12v to the wires directly emerging from the motor, then I would say you have a motor problem. Blower motors for some NT models are available for about $120 here, for example:
RV Furnaces and Parts

On the other hand, rather than spend hundreds of dollars on a rebuild with new time delay relay, sail switch, limit switch, gas valve and ignition board and igniter, when I suspect the heat exchanger will be heavily corroded, I would much rather install a new furnace, for about $420, as shown on the link above.
Nick.

PizzaChop · 08-18-2007, 04:05 AM

Having installed two NT 30s in two different 70's units, I agree with Nick. You'll be much happier in the long run if you just replace it.

You may find this thread of interest. The ending is kind of scary.

I too spent a few hours trying to salvage "original equipment" and after dumping all the rust and corrosion out of the burner chamber, I took it to an RV dealer. Upon inspection, they discovered that the main valve was leaking and allowing gas into the chamber continually and the danger was exactly such an explosion. They contacted Suburban to try to order the valve and were flatly told to trash the furnace, as the parts hadn't been produced in years and it was unsafe to operate. After reading the above thread, I'm just glad I didn't push it.

It is nearly 30 years old (assuming it was the original) and by the time you end up fooling around with it, you'll have more time invested in it than if you'd just replaced it. (The peace of mind is wonderful!)

Do a search for Suburban furnace replacement and you'll find pictures to help you. I paid a little less than above quote for new furnace from Palomino. PM me if you want more info.

wacnstac · 08-18-2007, 09:53 AM

Ron,

Have you ever replaced a NT30-MA? If so with what and, what kind of retrofits did you have to make? I'm wondering if I can put a NT30-SP into the old NT30-MA body and save myself some moving of ductwork, although I will still have to move the gas line.

Steve

john hd · 08-18-2007, 10:17 AM

before attempting to repair your furnace please read all of this thread.

http://www.airforums.com/forums/f427...0ma-35151.html

john

PizzaChop · 08-18-2007, 11:32 AM

Steve,

I don't know if they're an exact match or not. I'd be surprised if you didn't have to make a few modifications. I replaced an NT-32A and used the housing, except for the front of it.

On the Overlander, I replaced it without removing the galley. On the Sovereign, I had the galley out of the way. I have some more detailed pictures if you need them of what I did to make it fit.

Email me at pizzachop@alltel.net if you need to see them.

Here's a thread with a few pictures attached. I also have a couple in my Members Photos section.

mikeandbecky · 08-18-2007, 06:15 PM

Well, after removing the furnace, and discovering at least, the first of what may be possible many, problems with the old rusted NT 30MA, the fan motor, Ive decided to plug the inlet line, and at least until next year, rely on our back up ( a very capable Olympian 6100 BTU cat. heater that the PO had mounted at the front entrance( on the side of the oven/ furnace cabinet).

Looks like Ill be 'engineering' a new furnace in its place in the future. I dont think its worth the expense or risk with the shape my old one is in.

nickcrowhurst · 08-19-2007, 01:00 AM

Mike, my apologies if you are aware of the fact that catalytic heaters deplete the oxygen in the trailer. Then, when the oxygen is depleted, the combustion products will include carbon monoxide, a colorless and odorless killer. Long term memebers of this forum may recall that I once walked into a room on Christmas Eve and found a mother and daughter dead in their chairs, watching TV. The furnace flue was leaking.
If you type "catalytic monoxide" into the search box above you will get 14 threads to study.
I would recommend adequate ventilation and a good carbon monoxide detector. I would also never allow anyone to sleep while a catalytic heater was running.
Perhaps I am, understandably, a little paranoid about carbon monoxide.
Nick.

mikeandbecky · 08-20-2007, 03:54 PM

Thanks Nick. I am aware of the dangers. My intention is to replace the old furnace and that will likely occur within the next few monts. Pehaps after X-mas.Until then the only real use I'll be getting out of her will be a late October hunting trip to Montana. And then, I will be relying on an electric powered space heater, with intermittent use of the catalytic heater during the hours Im awake, if at all. As a law enforcement officer, Ive seen instances when carbon monoxide has killed, both by accident, and other situations. Its certainly nothing to take lightly! But I think Cat heaters do serve a purpose, and they are a great back up, if you are careful.